1. Field of the Invention
The present invention relates to a receptacle structure for optical sub-assembly for transceivers, which is able to increase optical coupling efficiency.
2. Description of the Related Art
In an optical fiber communication system, optical sub-assembly for transceivers is an important medium for conversion between optical signals and electrical signals. The optical sub-assembly for transceivers can be classified into transmitting optical sub-assembly (TOSA) for transmitting optical signals, bi-direction optical sub-assembly (BOSA) capable of receiving bi-direction signals in the same optical fiber and tri-direction optical sub-assembly (TRI-DI OSA) capable of receiving both digital signals and analog signals and transmitting digital signals. Either of the TOSA, BOSA and TRI-DI OSA has a receptacle structure in which an optical fiber module can be plugged to achieve optical coupling alignment for transmitting optical signals.
As shown in FIG. 1A, the receptacle structure 10 includes a receiving tube 11, a base seat 12 coaxially disposed in the receiving tube 11 and positioned at a bottom of the receiving tube 11, a sleeve 13 coaxially disposed in the receiving tube 11 and the base seat 12, and a fiber stub 14 coaxially disposed in the base seat 12 and the sleeve 13. An optical fiber 15 is arranged in the fiber stub 14. The bottom face of the fiber stub 14 is an inclined face 16 for preventing reflection light from being incident on a light-emitting element 17 so as to avoid interference of noises with the light-emitting element 17.
Referring to FIG. 1B, as to geometrical optics, the calculation formula of angle of emergence of light beam is as follows:n SIN(θ1)=SIN(θ1+θ2), wherein:    n: refractive index of optical fiber;    θ1: grinding angle of optical fiber on the end face of the fiber stub; and    θ2: angle contained between the axis of optical fiber and the direction of emergence of the light.
In the above arrangement, the fiber stub 14 is disposed in the base seat 12 in an upright state. In this case, according to the above formula, the direction of incidence of optical signal of the light-emitting element 17 is collinear with the optical fiber 15 rather than coaxial with the direction of emergence of the light of the optical fiber 15. Therefore, according to the theory that an optimal path is achieved when the direction of incidence of light and the direction of emergence of light, (that is, angle of incidence of light and angle of emergence of light), are coaxial with each other, this will cause loss to incident optical signal and needs to be overcome.